1. Field of the Invention
The present invention relates to a method of manufacturing an organic electroluminescent display.
2. Description of the Related Art
Organic electroluminescent displays (hereinafter, also referred to simply as “organic EL displays”) are expected as alternatives to the currently prevailing liquid crystal displays, and are under development for practical application. In particular, active matrix type organic EL displays having thin film transistors (TFTs) as switching elements are regarded as the mainstream of next-generation flat displays.
FIG. 1 is a plan view of an organic EL display having organic electroluminescent devices (hereinafter, also referred to simply as “organic EL devices”) for emitting luminescence in red, green, and blue with their respective pixels. FIG. 1 schematically shows pixel areas of the three colors mentioned above. Starting from the left, there are provided a red pixel Rpix having a red luminescent layer, a green pixel Gpix having a green luminescent layer, and a blue pixel Bpix having a blue luminescent layer.
Each single pixel is formed in an area surrounded by gate signal lines 51 and drain signal lines 52. A first TFT 130, a switching element, is formed near the upper left intersection of the signal lines. A second TFT 140 for driving the organic EL device is formed near the center. Organic EL devices are formed discretely in areas where hole injecting electrodes 12 are formed.
In general, an organic EL display comprises organic EL devices in which electrons and holes are injected into a luminescent layer from an electron injecting electrode and a hole injecting electrode, respectively. The electrons and holes recombine with each other at the interface between the luminescent layer and a hole transporting layer, near the interface, or inside the luminescent layer, thereby bringing organic molecules into an excited state. These organic molecules return from the excited state to a ground state with fluorescence emission.
Here, in forming the organic EL devices, the material of the luminescent layer can be selected to obtain organic EL devices for emitting luminescence in appropriate colors. Besides, such organic EL devices can be selected appropriately to achieve a color display.
In many cases, these organic EL devices are formed by vacuum evaporation. Moreover, in view of productivity, the organic EL devices are often manufactured by a batch method. When organic EL devices are manufactured by a batch method, the luminescent layers and the electron transporting layers are typically formed in different formation chambers of a system. This lengthens the time that elapses from the formation of the luminescent layers to the formation of the electron transporting layers thereon. Consequently, impurities responsible for degradation of the organic EL devices, such as water molecules and oxygen molecules, can get into the interfaces between the luminescent layers and the electron transporting layers.